A polysilicon thin film is a new functional material that has the advantages of both a crystalline silicon material and an amorphous silicon material, and it has the merits of high mobility of a monocrystalline silicon material and the merits of an amorphous silicon material that it can be manufactured in a large area and at low costs simultaneously. Therefore, studying on polysilicon thin film materials draws more and more attentions
A polysilicon thin film is composed of many small grains with different sizes and different crystal orientations. The grain size is generally in nanometer level such as tens to hundreds of nanometers, and the size of large grains may reach microns level. A polysilicon thin film with large grains has a relatively high mobility, which is close to the mobility of a bulk material. The polysilicon thin film has been widely used in manufacture of semiconductor devices, such as polysilicon thin film transistors (TFTs) in the display industry, micro-electromechanical systems, integrated circuits, and it may replace the SOI (Silicon on Insulator) material, or the like. In the display industry, especially in products of AMOLED (Active Matrix Organic Light-emitting Device) and TFT-LCD (liquid crystal display), in order to improve the performance of display panels, TFTs are usually used for manufacturing driving circuits of pixel and their peripheral areas. For most of the TFTs, polysilicon thin films are used as active layers, and moreover, driving circuits and display elements are both formed on a transparent glass substrate. In each of these cases, it is required that the polysilicon thin film has better performance. Further, the polysilicon thin film has high photosensitivity in the long-wave band, can effectively absorb visible light, and has the stability under illumination, and moreover, it does not have the light-induced degradation phenomenon of the amorphous silicon material, so that it is an ideal material for solar cells.
There are many methods for manufacturing polysilicon thin films in prior art, which including direct deposition methods and indirect crystallization methods. Direct deposition methods include a chemical vapor deposition method, a liquid phase growth method and a hot wire method, etc. Indirect crystallization methods include an excimer laser annealing (ELA) method, a solid phase crystallization method and a metal induced crystallization method, etc. However, the characteristics of the polysilicon thin films formed by above methods are not good because the polysilicon grains are rather small. Currently, in the production of polysilicon thin films, excimer laser annealing method is used most commonly as a low-temperature fabricating technology of polysilicon thin films. However, excimer laser belongs to a kind of pulsed laser and energy density of each pulse will vary somewhat, and so, it is uneasy to control the excimer laser in energy density, which brings about non-uniformity in sizes of final grains. In turn, this results in the fact that polysilicon thin films are not good in homogeneity. Moreover, the produced polysilicon thin films have relatively poor repeatability and stability, and are hard to be crystallized in a large area in manufacturing. There is still a demand for producing high-performance polysilicon materials.